1. Field of the Invention
The present invention relates to analog-to-digital converters (ADCs), and more particularly, to an error measuring method for a digitally self-calibrating pipeline ADC and an apparatus thereof.
2. Description of the Prior Art
A pipeline analog-to-digital converter (ADC) is a typical choice for high speed and high resolution analog-to-digital conversion. Without using any trimming techniques or calibration techniques such as analogue calibration or digital calibration, the resolution of the pipeline ADC approaches only up to a degree of ten to twelve bits. This resolution limit is mainly due to reasons such as capacitance mismatch induced during manufacturing or a limited gain value of operational amplifiers in the ADC. Additional circuitries or calibration techniques are required for implementing a pipeline ADC having a higher resolution of more bits.
Please refer to U.S. Pat. No. 5,499,027 and U.S. Pat. No. 6,369,744. In the two patents mentioned above, pipeline ADCs including digitally self-calibrating functionality and related circuits thereof are disclosed. According to the above-mentioned patents, an ADC includes a pipeline structure. The pipeline structure includes a plurality of stages of analog-to-digital conversion units including an input stage and a plurality of subsequent stages. In order to calibrate a specific stage of the analog-to-digital conversion units to eliminate errors due to the limitations mentioned above, the ADC further includes a calibration unit corresponding to the specific stage of the analog-to-digital conversion units. The ADC utilizes conversion units of later stages of the analog-to-digital conversion units, the calibration unit, and a set of calibration parameters corresponding to the specific stage of the analog-to-digital conversion units to calibrate such specific stage of the analog-to-digital conversion units.
In a calibration setup mode, the set of calibration parameters are derived from setting input signals of the specific stage of the analog-to-digital conversion units to predetermined values, recording output values of the later stages, and performing proper calculations. Through this design, the set of calibration parameters are measured under the same conditions as that of a run mode, so as to precisely represent errors inherent in the circuitry of the ADC.